The present invention concerns a method for impregnating wooden items against attacks from Teredo, particularly poles situated in marine environment.
Teredo is the Latin term for the family of shipworms that mainly live in salty water and mainly live off cellulose, which e.g. is found in wood. Shipworm is a long, worm-shaped bivalve, the shell of which only covering some of the front end of the animal.
Shipworms are active in the entire submerged length of the pole, i.e. from over the bottom to the surface zone. Attack by shipworms often only appears as small holes into which the larvae have disappeared. In the first year, shipworms are male, then changing to female. Reproduction occurs by male and female worms releasing semen and eggs to the water, after which fertilisation and hatching occurs freely in the water. When the larva is hatched, it seeks out a wooden item in the water, including poles and the like. The larva bores into the e.g. pole and lines the passage with a thin layer of lime. In the larva stadium, the shipworm larva is feeding mainly on cellulose fibres from the pole in which it has been born while at the same time eating and growing so that the destructive effect on the pole becomes more and more comprehensive. Thus it is difficult to judge to which extent a given pole is attacked by Teredo.
In order for the Teredo family of shipworms to live, a certain water temperature, a certain saltiness, and wood must be present. In the warmer areas of the Mediterranean Ocean, shipworm attacks have been widespread for a long time, and in recent years the attacks have also spread to Danish waters.
In order to counteract and curb attacks from Teredo, one may use exotic wood species for one's poles, including e.g. cypress wood, jarrah wood, turpentine wood. These and a few other types of wood are naturally resistant against Teredo attacks, but are very rare species of wood as well as they are very expensive. Degrading of the wood cannot be avoided, but the service life of the pole can be prolonged.
Another way of preventing Teredo attacks is to impregnate with chemical means. Since most chemical agents are environmentally hazardous, there is a desire to reduce the use of environmentally harmful agents as these are leached out into the sea water and thereby have negative effect on the marine environment around the pole.
A third method is to use mechanical or chemical barriers. A kind of mechanical barrier is to coat the pole with a copper layer or a concrete layer. This is a costly and cumbersome method, which in many cases makes it advantageous from an economic point of view to let the pole stand untreated, and, when the pole is degraded by Teredo attacks, to substitute it with a fresh pole.
A fourth method for preventing Teredo attacks is to coat the pole externally with a chemical barrier, e.g. in the form of a plastic film impregnated with a chemical material. This method has the same disadvantages as the chemical impregnation of the pole as often there are released very poisonous substances to the surrounding marine environment with associated harmful effects.
Thus there exists a need for producing a cheap and secure impregnation of wooden poles, whereby it is ensured in an environmentally safe way that the poles are safe-guarded against attacks from Teredo.